Shark attacks on humans have been recorded from ancient times. One such attack on an unlucky Mediterranean sponge diver is recorded from the third century B.C. (Thomas B. Allen, Shark Attacks: Their causes and avoidance 35 (2001)). And since the early part of the twentieth century, the populace of the United States has been riveted by sporadic stories of sensational and gruesome human encounters with sharks. As the twentieth century progressed and America's love for the seashore grew, so did its fascination with the remote but real possibility of a dangerous brush with one of these creatures. From at least 1916, shoreline municipalities began to develop physical structures to keep public bathing areas safe from the perceived danger of sharks. And through the present day, reports of shark attacks have frightened coastal communities and negatively impacted their economies as seashore revelers curtailed their beach excursions with each new and ever frightening story of voracious sharks in a particular town's waters.
As the number of humans spending time in the ocean has increased, so has the number of shark attacks and along with that increase in attacks so grows the urgent need for a repellent. Further, as the twenty-four hour news cycle continues its frenetic discussion of the threat of sharks to humans, each shark attack in the developed world appears to be reported with greater sensation and grander desperation. As such, the ever-pressing need to develop an effective shark repellent is even greater than before as the public seeks to provide itself some assurance that it will not be a victim of the next injurious encounter with a shark.
While fear of attack by sharks seems to have appeared in the United States in the early part of the twentieth century, the Second World War particularly amplified this fear when U.S. service personnel were called to combat in the dangerous and “shark infested” South Pacific. During that time, the U.S. Navy began a concerted effort to develop a chemical shark repellent to protect sailors and air personnel exposed to sharks when downed in shark-prone waters. Since then, government and private industry have worked to discover and develop a chemical shark repellent potent enough to protect humans. (Johnson and Baldridge (1985).
To establish clear criteria for government development of an effective chemical shark repellent, Johnson and Baldridge set forth a goal in 1985 of finding a chemical that would repel sharks in ocean water at 1 part per billion. While the goal was a good one, no previously-developed chemical repellent has even come close to achieving the standard.
An effective repellent would not only provide some assurance to humans bathing or adrift in waters frequented by sharks, an effective repellent would also significantly help the commercial fishing industry. Commercial longline fishing operations routinely target swordfish and tuna. However, the longline fishing hook is not selective, and it is not uncommon for more sharks to be caught than swordfish or tuna. Sharks that are caught as unintended targets are commonly called “by-catch.” Often, the shark dies on the hook prior to retrieval. If a live shark is cut free during retrieval, the hook, snood and gangion are usually lost. This presents significant monetary loss as well as significant inadvertent death for millions of sharks. There has been a long-felt need to reduce by-catch losses in the fishing industry and to save the lives of many millions of sharks each year. Currently, as many as 80 species of shark are considered threatened with extinction and it is estimated that up to 100 million sharks are killed each year by humans. It is no surprise, then, that an effective repellent would satisfy a long-felt need in the commercial fishing industry.
It has been recognized for some time that development of a repellent effective against two particular orders of shark, Carcharhinoforme and Lamniformes, would provide considerable protection to humans and considerable assistance to commercial fishing. This is because nearly all of the known aggressive species of sharks and the predominant kinds of sharks that also interfere with commercial fishing are from those two orders. Orders Squaliformes and Orectolobiformes, on the other hand, represent sharks that have caused relatively few injuries throughout history and do not commonly harm commercial fishing interests.
Sharks and their close relatives, rays and skates, are classified in biological taxonomy within the class Chondrichthyes (fish) and the sub-class Elasmobranchii (fish without bones). Within the sub-class Elasmobranchii, sharks are classified in the sub-class Selachii, and rays and skates are classified within the sub-class Batoidei.
Of the more than 350 known species of shark, as many as 35 species have been recorded attacking humans. Repeated attacks, however, have been recorded with less than 15 of these species. The frequency of shark attacks worldwide is quite small compared to the number of humans who work and play in the ocean each day. Less than about 100 humans are attacked by sharks each year with fatalities from shark attack averaging around 30. Nevertheless, the real fact of shark attack and the constant possibility, though low probability, of shark attack makes the need for an effective shark repellent a pressing reality for millions of ocean-going people every day.
While fatal shark attacks have most likely occurred for millennia, recorded events have been rare until the twentieth century. One early recorded fatal shark attack occurred in 1580 when a man overboard on a Portuguese sailing vessel was reportedly “torn to pieces” while clinging to a life buoy. (Allen (2001) at 33). This was certainly not the earliest recorded shark attack. In fact, the danger of shark attacks on sponge divers in the Mediterranean was documented in the Natural History of Pliny the Elder in 77 A.D. and the above-noted fatal story of a sponge diver who lost part of his lower body to a shark was recorded in the third century B.C. (Allen (2001) at 35). Many shark attacks have been recorded ever since. There appears, however, to have been no consideration of methods of limiting shark attacks (at least in the United States) until 1916.
The summer of 1916 ushered in “the year of the shark” for the coastal regions around New York City. Over just 12 days in that summer, at least four people were killed by sharks along the New Jersey coastline. (Allen (2003) at 174). These attacks later inspired the movie Jaws (1975). (Thomas B. Allen, The Shark Almanac 174 (2003)). Beginning in 1916, the American public embraced a collective and long-enduring fear of sharks. This fear swelled to a point of concern for the U.S. government when it entered World War II against Japan in the South Pacific. (Allen (2001) at 207). To maintain morale among sailors and airmen (and their families) who faced the constant possibility of finding themselves adrift and exposed at sea, the U.S. government began research directed at protecting service personnel from shark attack. (Allen (2001) at 207). In this effort, the U.S. Navy began a program to develop a chemical shark repellent. The resulting product was known as “Shark Chaser.”
In Chapter 17 of Dr. Perry W. Gilbert's 1975 printing of “Sharks and Survival”, Richard L. Tuve of the U.S. Naval Research Laboratory describes the development of the U.S. Navy “Shark Chaser” chemical shark repellent. The program originated with the Office of Strategic Services in March 1942. Initial research was based on anecdotal evidence; Floridian fishermen contended that if a shark died on an unattended hook and line, further fishing in that area became undesirable. The researchers, therefore, hypothesized that some substance emitted by the decomposing body drove other sharks away from the vicinity.
As research continued, Woods Hole investigators and U.S. Navy scientists determined (erroneously it turns out) that the principal chemical material exuding from the decomposing shark was ammonium acetate. Scientists at Wood Hole also proposed the use of copper, which was known to reduce feeding in captive fishes and sharks. The ultimate combination of ammonium acetate and copper produced copper acetate, which was combined with nigrosine dye to provide a visual indication of the repellent dispersion.
The dye and copper acetate combination was molded into cakes and field testing began in 1944. Following a series of successful tests, a readjustment to 20% copper acetate and 80% nigrosine dye cake was sold as the “Shark Chaser.” The military specifications for “Shark Chaser” were given under MIL-S-2785A as of Feb. 2, 1961.
As the Shark Chaser repellent found widespread use, continued research revealed that copper acetate was not effective in repelling sharks. In Chapter 2 of Bernard J. Zahuranec's 1983 printing of “Shark Repellents from the Sea: New Perspectives” the author gives insight into the inefficacy of the Shark Chaser. From tests in the shark pens at Bimini, Bahamas, Gilbert and Springer (1963) concluded that copper acetate fails to repel or inhibit the feeding activities of several species of sharks we have worked with at Bimini. Tester (1963) also reported the inefficacy of copper acetate against tiger sharks and other fish. Some theorized that the nigrosine dye itself was actually a visual deterrent. It was eventually concluded that copper acetate was not a practical deterrent for human use, and the military ultimately halted the issuance of the Shark Chaser. Recent research by the present inventors has confirmed these earlier findings that copper acetate is ineffective as a shark repellent and that ammonium acetate is not a principal component of decomposing shark tissue. See Tables 2 and 4 and FIG. 8.
While copper acetate was abandoned by the U.S. government in the 1960s, shark repellent research continued in the United States, with focus on marine organisms as sources of a repellent. Holothurins, anemones, urchins, and gorgonians were explored for a potential toxin but no shark repellent activity was detected. More research has been conducted on other naturally-occurring compounds. The inventors report that holotoxin from macerated sea apples, as well as seven types of potent hemolytic glycosides (saponins) from plants, were not effective as shark repellents.
Over the last 50 years antishark measures employed to protect humans from shark have included electrical repellent devices (Gilbert & Springer 1963, Gilbert & Gilbert 1973), acoustical playbacks (Myrberg et al. 1978, Klimley & Myrberg 1979), visual devices (Doak 1974) and chemical repellents (Tuve 1963, Clark 1974, Gruber & Zlotkin 1982). None of these procedures proved totally effective in preventing shark attacks. (Sisneros (2001)).
Following World War II, when reports of Shark Chaser's ineffectiveness began to appear, the Office of Naval Research began to reconsider the matter of chemical shark repellents and renewed the screening and testing of possible candidates (Zahuranec & Baldridge 1983). Hundreds of chemical substances were tested on sharks in an effort to find a chemical that would produce a quick and effective repellent response (Springer 1954, Gilbert & Springer 1963, Tester 1963). These chemicals included powerful toxins that could (and did) kill a shark after brief exposure; but none elicited the desired repellent response. Support for the research eventually ended after many attempts had provided no effective shark repellent. (Sisneros (2001)).
As described in the ReefQuest Centre for Shark Research:                In 1974, ichthyologist Eugenie Clark noticed that the delicate Moses Sole (Pardachirus marmoratus) was easy to catch and appeared to secrete a milky, astringent substance from the base of its dorsal and anal fin spines. Suspecting that the little fish was protected by a toxin of some kind, Clark collected several specimens for study. She found that the Moses Sole did indeed secrete a toxin she named “pardaxin,” which caused red blood cells to rupture and—most intriguingly—repelled sharks. Tests by Clark in the laboratory and open sea revealed that at least four species of sharks were repelled by pardaxin for 10 hours or longer.        
While fresh pardaxin repelled sharks, it presented serious stability problems because it was not stable for room temperature storage, and was heat-sensitive. Pardaxin could be freeze-dried, but this form was only 30% as effective as the fresh secretion, as reported by Zlotkin (1976). Chemical analysis yielded that pardaxin was an acid protein of 162 amino acids with a MW of 17,000 Daltons. The acid protein had a difficult synthesis pathway making commercial production not commercially practical. Sigma-Aldrich currently offers pardaxin for sale in the U.S. at $487.00 US for 1 milligram (product #P0435-1MG). Similar compounds such as mosesin and pavoninin present the same difficulties. There has been and remains a long-felt need for a shark repellent that can be produced and stored at room temperature with high yields of repellent. Further, it is believed that pardaxin, mosesin, and pavoninin act on the shark's respiratory system, requiring a minimum concentration of repellent to enter the mouth and contact the gill rakes of the shark, i.e., repellent had to be squirted directly into the shark's mouth.
Zlotkin noted that pardaxin possessed surfactant properties, reducing surface tension by as much as 60%. As described at the ReefQuest Centre for Shark Research:                Zlotkin teamed with shark biologist Samuel Gruber to test a hunch: could commercially available soaps repel sharks? Zlotkin and Gruber tested two inexpensive commercial soap components, sodium and lithium lauryl sulfate (SLS and LLS, respectively—SLS, incidentally, is a common ingredient in shampoos), on young Lemon Sharks (Negaprion brevirostris). They found that both compounds were even more effective than pardaxin at repelling captive Lemon Sharks.Further tests by Nelson et al. found that SLS was an effective repellent against blue sharks and even great white sharks. As described in “The Behavior and Sensory Biology of Elasmobranch Fishes: An Anthology in Memory of Donald Richard Nelson” (Tricas, T. C. & S. H. Gruber (ed.) (2001)), as well as “Surfactants as chemical shark repellents: past, present, and future” (J. A. Sisneros (2000)),” the greatest limitation of SLS is that it is required to be squirted into the mouth of an approaching shark. It is not effective in surrounding-cloud-mode dispersions. Therefore, SLS is only useful when the user can clearly see an approaching shark and orchestrate the delivery of SLS into the animal's mouth. There has been a long-felt need for a repellent administered in surrounding cloud dispersions, thereby avoiding the impracticable need for direct-oral delivery.        
In 2001, Sisneros reported further research on compounds related to pardaxin. Sisneros confirmed that dodecyl sulfate was the most effective surfactant shark repellent available at the time and that even the best repellent did not meet the Navy's potency requirement for a nondirectional surrounding-cloud type repellent of 100 parts per billion (0.1 ppm or 100 micrograms/Liter). Sisneros further concluded that dodecyl sulfate would only be practical as a directional repellent such as in a squirt application. Sisneros suggested that future research should test the action of alkyl sulfates on cell membranes, the potential of other biotoxic agents, and semiochemicals in the search for an effective chemical shark repellent. (Id.)
The existence of semiochemical repellents were first considered by Rasmussen & Schmidt in 1992. They suggested that sharks may be chemically aware of the presence of potential danger by sensing the bodily secretions from potential predators. Rasmussen & Schmidt hypothesized that lemon sharks, especially juveniles, inherently recognize chemical exudates produced by the American crocodile, Crocodylus acutus, a known predator of sharks. The concentrations needed to produce aversive responses in lemon sharks ranged from 10-7 to 10-9 M, which was near the functional limit of shark chemoreceptors (Hodgson & Mathewson 1978).
Sisneros also noted that another proposed potential source for shark repellent semiochemicals might perhaps be found in decomposing shark flesh (Baldridge 1990, Rasmussen & Schmidt 1992) because anecdotal information from fishermen claimed that sharks avoid areas containing decomposing carcasses of previously caught dead sharks. Sisneros postulated that perhaps there are semiochemicals found in extremely low concentrations in decaying shark flesh that act as alarm pheromones and provide warning signals to nearby sharks. None of those postulated compounds were known or have since been found and there have been no commercially available effective chemical shark repellents. As such, the long felt need for an effective repellent had not been satisfied until the present invention.
U.S. Pat. Nos. 4,490,360 and 4,340,587 describe the use of lucibufagins from fireflies and extractions of fireflies as a shark repellent. While the specifications suggest that behavioral changes were occurring in numerous species of animals, no effects were observed on larger inshore and pelagic sharks. Further, while one specification describes the “very extensive practical use in protecting bathing zones from the invasion of objectionable sea life such as sharks,” the Atlantic Sharpnose species represents a very small-sized inshore species which has no reported aggressiveness nor represents a bycatch problem. Additionally, no practical synthesis is described for lucibufagins, therefore tremendous quantities of fireflies are required to produce drum-quantities of a repellent.
Data on the use of firefly-derived repellents were also reported against the Atlantic Sharpnosed Shark (Rhizoprinodon terraenovae), the smooth dogfish (Mustelus canis), the pinfish (Lagadon rhomboides), and killifish (Fundulus heteroclitus) in a paper presented at a symposium in 1981. (Bonaventura et al., Problems and Possibilities: The Development of an Effective Shark Repellent for Naturally Occurring Biologically Active Substances, Jan. 5, 1981, Annual Meeting of the American Association for the Advancement of Science, Toronto, Canada). These data additionally provide no support for a repellent of inshore and pelagic sharks that would be useful as an effective shark repellent.
U.S. Pat. No. 6,606,963 describes an acoustical system which produces shark-repelling waveforms. This invention affects the shark's hearing and lateral line sensory systems. However, as described by Klimley, Myrberg et al., sharks rapidly habituate to a sound source unless output power is very high. The present invention overcomes these limitations by, in theory, affecting the olfactory system. There has been a long-felt need for a repellent that is effective such that competitively feeding populations of sharks will stop feeding and will avoid all food stimuli in the presence of the repellent, wherein no habituation is observed after exposure.
Researchers have historically used several bio-assays to determine if a repellent evokes a flight response in shark. One such bio-assay introduces repellent of a certain concentration and volume to a position in a tank and measures avoidance in sharks of that portion of a tank or other aversive swimming behavior.
Another such bio-assay introduces repellent of a certain concentration and volume into the feeding zone of sharks and measures whether sharks flee the feeding zone and/or cease feeding behavior.
Another preliminary bio-assay measures the effect of a repellent on a shark that is immobilized in “tonic immobility.” Tonic immobility is a state of paralysis that typically occurs when a shark is subject to inversion of its body along the longitudinal axis. This state is called “tonic,” and the shark can remain in this state for up to 15 minutes thereby allowing researchers to observe effects of chemical repellents. After behavioral controls are established, an effective chemical repellent will awaken a shark from a tonic state. Researches can quantify dose sizes, concentrations, and time to awaken from these studies. A microliter autopipettor is used to observe effects at the 10-100 uL level. A 60 cc syringe is used as a baseline, looking for a preliminary response.
Another bioassay is known as the Johnson-Baldridge test. The test is defined as the delivery of 100 mg of chemical repellent into a 6 cubic meter boundary of water over a 3.5 hour period under steady-state conditions. This level of repellent delivery from a point source is considered to represent a concentration of 0.1 ppm. This is a proposed criterion in the art for an “effective” repellent. If sharks demonstrate aversive behavior under these conditions, then the criteria is satisfied. The inventors have designed and constructed an experiment to test if semiochemicals meet the Johnson-Baldridge criteria. A PVC tripod was situated in the ocean. The tripod supported a peristaltic metering pump, set to meter out exactly 100 mL of repellent per hour. The tripod also supported a video camera and transmitter, which observed the area under the tripod, marked off for 6 cubic meters and compensated for tidal changes. The video was monitored and recorded on shore. A fish head was secured under the tripod, within view of the camera. Once a population of sharks was established near the tripod, a control was performed. A second fish head was secured, the pump was started, and behavior was observed. If the fish head was protected for the 3.5 hour period, the criteria were met.